Glassfish is still the reference implementation for Java EE (in other words, it is supposed to demonstrate how an official Java EE application server is supposed to implement the standard).

As far as I understand it from what I hear on Oracle's Java podcast, Glassfish is meant to be the Java EE implementation that first implements the newest standards, while for example Weblogic is meant to be the "proven technology" implementation: it won't implement the very latest Java EE standard immediately, but it will be better tested and more "proven" than Glassfish.